Employing organic donor-acceptor thermally activated delayed fluorescence (TADF) compounds as photocatalysts

Abstract

This thesis aims to expand the range of donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) compounds trialled as photocatalysts (PCs), as well as increasing mechanistic understanding of photocatalytic processes. Chapter 1 describes the fundamental photophysical and photochemical processes that underpins the reactivity of the PC. A literature review of the relevant examples of TADF emitters as PCs is presented.

Chapter 2 focuses on testing a D-A TADF compound outside of the carbazolyl dicyanobenzene family, pDTCz-DPmS, as a PC across a range of mechanistically distinct, literature known, photocatalysis reactions, with the performance cross-compared to the popular TADF PC, 4CzIPN. Across most reactions, pDTCz-DPmS provided similar yields to 4CzIPN.

Chapter 3 details the modification of the TADF emitter DMAC-TRZ by the addition of a Hammett series of five para-substituted phenyl moieties to the DMAC donor group, developing strongly photoreducing compounds capable of promoting the photoinduced dehalogenation of aryl halides (up to E_red = -2.72 V vs SCE). However, mechanistic investigations suggest that the DMAC-TRZ compounds photodegrade under the reaction conditions, with the resultant photodecomposition product likely responsible for the photocatalysis.

Chapter 4 delves into the complex issue of the influence of solvent in photocatalysis. The optoelectronic properties of eight PCs (TADF and non-TADF) were acquired in a range of polarity solvents, and the PCs were subsequently trialled in several photocatalysis reactions to correlate trends in optoelectronic properties with yields. Surprisingly, no such trend could be found. Instead, all PCs were found to photodegrade in electron transfer photocatalysis, while were photostable in energy transfer photocatalysis.

Chapter 5 employs the previously identified TADF PCs in the development of the photocatalytic functionalisation of 1,3-diones to form 2-aryl-1,3-diones. Although some preliminary results were promising for acyclic 1,3-diones, the protocol was not successful for cyclic 1,3-dione systems, which are of greater interest to the agrochemical industry.

Date of Award	13 Jun 2024
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Eli Zysman-Colman (Supervisor)